The invention relates to a transport mechanism for disk-shaped workpieces, in particular for semiconductor wafers.
In modern vacuum process facilities circular flat substrates or workpieces, which are also referred to as wafers, are surface treated, such as for example coated, etched, cleaned, thermally treated etc., in such fully automated vacuum process systems. In order to automate such processes and to be able to carry out multi-stage processes in different facility areas, automated transport systems, a type of handling robot, are employed. In particular the treatment of semiconductor wafers in such processes requires very high quality of treatment, such as in particular high cleanliness, high precision and careful treatment of the substrates. Due to the stated high requirements, such facilities preferably include a lock chamber, where the wafers are moved from the atmospheric environment into a vacuum chamber and subsequently into a process station or, as a rule, sequentially into several process stations in order to be able to carry out the required surface treatment. With the aid of a transport device the wafers are delivered in a horizontal transport plane from the lock chamber into the process chamber, and after the wafer has been deposited in the process chamber, the latter is, as a rule, closed in order to be able to carry out the process under the required vacuum and process conditions. If several process steps are necessary, the wafer is again transported out of the one process chamber in the same manner and, for the next process step, is transported into another process chamber. Especially preferred types of facilities are so-called cluster systems. In such systems, the lock chamber and the process chamber, or the several chambers, are arranged peripherally about the substantially central transport chamber. In the case of more than one lock chamber and in particular in the case of several process chambers, these chambers are arranged in a type of star-shaped configuration about the centrally located transport chambers. The transport device in this case is located in this centrally located transport chamber and has access, on the one hand, to the at least one lock chamber and, on the other hand, to the process chamber. Between the transport chamber and the remaining chambers conventionally and preferably a so-called lock valve is disposed in order to be able to partition the chambers against one another during the locking process or during the process step. During the transport process of a wafer, the transport device subsequently extends appropriately through the open lock gates in order to deposit the wafer at the designated location.
The transport device moves the wafer translatively in one plane and consequently in two directions of motion. In said preferred cluster systems with the transport device disposed in the central transport chamber, the device is conventionally formed as a mechanism which pivots about a center of rotation and forms therewith the one rotating direction of motion and which can execute a further second translatory motion radially with respect to the center of rotation back and forth away from/to this center of rotation. On this transport device, for example a length-adjustable arm mechanics rotatable in the horizontal plane, the wafer to be transported is subsequently deposited in the end region of this arm. Such a configuration can in this case readily also transport a wafer over relatively great path distances, for example of the orders of magnitude of 1 m or more, from a lock chamber into the transport chamber and from here, in turn, into and out of the process chamber and extend through the corresponding opened lock doors. At the beginning of the transport cycle the wafer is deposited under atmospheric pressure onto the transport mechanism as precisely as possible and always in the same position in order to be able to transport it subsequently also precisely to a predetermined position. However, the deposition of the wafer on the transport mechanism, as well as also the transport mechanism itself, is afflicted with imprecisions or with tolerance errors. Further imprecisions or shifts of the wafer position on the transport mechanism can also occur in the process station due to effects in the process chamber.
A particular problem in the handling of disk-shaped workpieces occurs if the workpieces are very thin relative to the diameter and deflect correspondingly strongly. This is in particular the case with semiconductor wafers, which have perhaps a thickness of a few tenths of a millimeter, such as preferably 0.07 to 0.3 mm at a diameter of 100 mm to 300 mm. Depending on the type of support the deflection may be in the range on a few tenths of a millimeter up to a few millimeters. This makes precise handling and positioning within a transport configuration considerably more difficult especially since the deflection can be of different magnitudes. Especially problematic is the handling or transfer of semiconductor disks from a cassette into the designated positions, such as process stations or chambers of a vacuum process facility. In such facilities the semiconductor wafers are deposited horizontally in magazines formed as cassettes and again removed horizontally from them, in order to intermediately store them on compact space. Special difficulties are encountered with wafers which deflect strongly, with respect to handling precision and desired compactness of the configuration and reliability of the handling.
EP 0 696 242 B2 discloses a transport mechanism for semiconductor wafers which permits lifting and depositing circular semiconductor disks, or disk-shaped workpieces, with the aid of a height-adjustable handling robot rotating about its axis with a carrying arm or carrying element extensible in the horizontal plane or to deposit them and bringing them into a different position. Therewith it is possible for example to remove workpieces with a transport arm from a cassette and transport them into a different position, where they can, for example, be worked. In vacuum process facilities the workpieces must be moved in and out through a lock, be that from atmospheric pressure into the facility or within the facility between different chambers. The previously described transport arm of the robot, if needed and under control, reaches through the corresponding lock gates for the transportation of the workpiece to the correct target location. Depending on the concept of the facility, for the intermediate storage of the workpieces cassettes are utilized which can hold several workpieces in a small space and can be employed either outside of the facility and/or inside the facility. The arrangement introduced in the patent permits realizing transport mechanisms of this type. The underlying assumption in these known transport mechanisms is that the workpiece remains flat as defined and that its dimensions are also defined. The handling as well as also the substrate acquisition with the appropriate electronic or optical sensors build on these prerequisites.
However, for large-area thin workpieces, which deflect strongly, considerable problems are encountered with this mechanism and a solution of them is not provided. In these cases such transport mechanisms are correspondingly functionally also operated at their limit, which decreases the operational reliability of such facilities.